Got a 2012 2WD double cab prerunner with the 2.7 I4/auto since it matches what we actually do with a truck (nearly no towing, a bit of light hauling and a lot of on-road driving). So far I'm loving it - enough power for anything I really do and certainly better mileage than my (t)rusty F-150 that it's replacing. And it looks good.
In a high headwind (20+mph) at freeway speeds (70 - 75mph), the engine is on the edge of what it will reasonably handle - putting it on cruise control pretty much locks it into a downshift, though you can manually drive it so that it stays in 4th and maintains speed. Gas mileage is in the 18-19 mpg range under these conditions.
What will happen if I put a cap (I'm looking at the Leer XQ100) on it? A slight reduction of mileage would be okay, but if I can't maintain freeway speed it won't be a good day. Flat bed covers aren't really an option since dry storage volume is needed.
Opinions are all over the place on this...anyone have experiences to share?